Deep freeze leech, or: the ultimate brain freeze

Recently, I spotted this graph on one of my social media platforms:

For those not familiar with the kelvin scale, 100 kelvin is -173°C. But soon after I saw this, I read a paper that is going to require a slight modification to this graph:

Meet the animal that forced the rewrite: Ozobranchus jantseanus.

This is a leech that lives on Japanese turtles. Some turtles can spend most of the winter under ice, so they get very cold, which in turn means anything on them will also get very cold. Cold is a problem for animals, for reasons you can see in this video:


The can is actually a good model for why freezing is bad for organisms. Water is weird: it expands when it freezes. If you think of the can as being like a cell, freezing causes all sorts of damage. Some species are able to tolerate freezing temperatures with biological antifreezes and other tricks.

But very fee are able to take it to the extreme of the leech above.

Suzuki and colleagues (2014) tested seven different species leeches, and froze then at -90°C.

Six of those species died. Ozobranchus jantseanus lived. Not only that, they could survive being frozen at -90°C for almost a year. And they could be frozen and thow out again up to five times before suffering any mortality.

Not content, Suzuki and colleagues decided to up the ante. They dropped these animals into liquid nitrogen, and left them there for 24 hours. All of them (tried with five individuals) revived when they were thawed back up, and lived over a month. Now, the animals that were frozen were not entirely normal. They couldn’t stretch the way they could before hand, but they were most definitely alive, moving under their own power.

This stunned me, and I thought for sure that this must be a record holder. But it turns out that there are a few other species that can take extreme temperatures, with the coldest being the larva of a fly (Polypedilum vanderplanki) that can survive a stunning -270°C. It does this by drying itself out completely, virtually becoming a living rock (“vitrifcation”).

How the leeches are doing this is not worked out at all in this paper. It must be some standing feature of the animal, because they are essentially flash frozen. There is not time for any sort of physiological or cellular response to kick in from a reaction to the cooling.

This is a very cool result (pun intended). One of the research groups that must be excited about this are the people interested in exobiology and the prospects of life on other planets. If something can survive these sorts of extremes, it significantly stretches the possible environments in which we might find life.

And this post gives me an excuse to feature one of my favourite movie musical numbers in years, this show stopper from Frozen:


Reference

Suzuki D, Miyamoto T, Kikawada T, Watanabe M, Suzuki T, Uemura M. 2014. A leech capable of surviving exposure to extremely low temperatures. PLoS ONE 9(1): e86807. DOI: 10.1371/journal.pone.0086807.t001